In recent years, there has been developed a nondestructive sensing technique using an electromagnetic wave (its frequency is in a range of 30 GHz to 30 THz) ranging from a millimeter wave to a terahertz wave. As for a technique using the electromagnetic wave having this frequency band, there are developed a technique for carrying out imaging using a safe penetrative inspection system instead of an X-ray system, and a technique for obtaining an absorption spectrum or a complex permittivity of the inside of a substance to evaluate a bonding state of atoms, or concentration or mobility of carriers. In addition, as for a technique using a millimeter wave, there is developed a position sensing technique for a collision safety radar having a frequency in 70 GHz band.
For example, as for a two-dimensional imaging system, there is a proposal example in which a system is configured with a millimeter wave generator, an antenna for radiating the millimeter wave, a reception element, a propagation path for the millimeter wave, and the like being used as discrete components (refer to Japanese Patent Application Laid-Open No. 2001-050908). This system is shown in FIG. 8. This system is designed such tat a millimeter wave 116 is radiated from a sinusoidal millimeter wave generator 102 to the space through an antenna 112, and the millimeter wave 116 having an intensity distribution is received by an electro-optic crystal 110 having light reflecting film 111 and directed by reflectors 109 through wave plates 107 and 108 to be read with a laser beam from a laser 104. The system also includes sinusoidal wave generators 101 and 103. At this time, a phase difference in the millimeter wave caused on the basis of a difference in permittivity of a specimen object 113 is detected by utilizing a synchronism wave detection technique and polarization beam splitter 106, photodiode 105, computer 114 and lock-in amplifier 115 to obtain penetrative imaging excellent in an S/N ratio.
On the other hand, as for the position sensing technique, an on-vehicle millimeter wave radar is in a progress of being developed for the purpose of measuring a distance between a forward vehicle and a backward vehicle. As for a proposal example thereof, there is a transmitter-receiver which is constructed in the form of a module as shown in FIG. 9 using a non-radiative dielectric Line (NRD) (refer to Japanese Patent Application Laid-Open No. 2000-022424). In this example, a millimeter wave outputted from a millimeter wave oscillator provided in an unmovable portion 232 is propagated through an NRD 221 to reach a primary radiator 213 provided in amovable portion 231 through a circulator 219 and couplers 212 and 211 to be received by a horn antenna (not shown) provided above the primary radiator 213. In this connection, the movable portion 231 is moved to be adapted to carry out the scanning for a radiation directional angle of the millimeter wave. After received by the same horn antenna, the millimeter wave is mixed with a millimeter wave which is obtained by a coupler 221 through the branch of a part of the millimeter wave from the oscillator, in a coupler 223 through the circulator 219. The module also includes transmission line 222 having termination devices 220. In such a manner, the millimeter wave concerned is received. From the foregoing, the millimeter module capable of making a detection direction variable is constructed.